1. Field of the Invention
The present invention relates to an organic light emitting display device and a method of fabricating the same, and more particularly, to an organic light emitting display device having an optimal (or improved) resonance structure and a method of fabricating the same.
2. Description of the Related Art
In general, an organic light emitting display device having thin film transistors for driving pixel circuits is an active matrix light emitting display device having a fast response speed as well as a wide viewing angle and excellent contrast, so that it has attracted attention as a next generation display device.
The organic light emitting display device is classified as either an inorganic electroluminescent (EL) display device or an organic EL display device according to materials used for forming an emitting layer. The organic EL display device has excellent luminance, drive voltage, and response speed characteristics, and displays many colors compared to the inorganic EL display device.
In addition, pixel regions defined by a plurality of scan lines and a plurality of data lines formed in a direction perpendicular to the direction of the scan lines may display red, green, and blue colors, so that the organic light emitting display device may constitute a full-color flat panel display device.
FIG. 1 is a schematic cross-sectional view of a conventional organic light emitting display device.
Referring to FIG. 1, the organic light emitting display device generally has a substrate 110 and an upper substrate 120 formed above the substrate 110. The upper substrate 120 covers (or encapsulates) the substrate 110 using an adhesive 130 or the like.
A red color pixel region (R), a green color pixel region (G), and a blue color pixel region (B) are disposed on the substrate 110 to display red, green, and blue colors, respectively.
A first electrode layer, an emitting layer, and a second electrode layer, which each have a predetermined pattern, are formed on the substrate 110 in each of the pixel regions. Several layers constituting each of the pixel regions are not shown in FIG. 1 for simplicity of description.
A hole injection layer and a hole transport layer may be formed as a common layer on the entire surface of the substrate having the first electrode layer. An emitting material corresponding to each of the pixel regions is stacked on the hole transport layer to form R, G, and B emitting layers.
A hole blocking layer, an electron transport layer, and an electron injection layer are sequentially formed on the entire surface of the substrate if necessary, and a second electrode layer is formed on the electron injection layer. In this case, the hole injection layer, the hole transport layer, the emitting layer, the hole block layer, the electron transport layer, and the electron injection layer are organic thin layers formed of an organic compound.
However, in a case of the full color organic light emitting display device, a difference between luminous efficiencies per pixel, i.e., per color, occurs. That is, the luminous efficiency of the green color emitting material is superior to those of the red and blue color emitting materials. In addition, the luminous efficiency of the red color emitting material is superior to that of the blue color emitting material.
Accordingly, there have been many attempts to obtain maximum efficiency and luminance by controlling the thickness of the organic thin layers in the related art. For example, Japanese Laid-Open Patent Publication No. 1992-137485 discloses a technique for enhancing the luminous efficiency by setting the thickness of an electron transport layer in a range of 30 to 60 nm in a structure sequentially having a positive electrode, a hole transport layer, an emitting layer, the electron transport layer, and a negative electrode.
In addition, Japanese Laid-Open Patent Publication No. 1992-328295 discloses a technique for substantially increasing the luminance by adjusting the thickness of an electron transport layer when light emitting from an emitting layer interferes with light reflected from a negative electrode. In addition, Japanese Laid-Open Patent Publication No. 1995-240277 discloses an organic light emitting display device for enhancing luminance and color purity of blue emission by controlling an optical layer thickness.
Such organic light emitting display devices set the optical thickness to be different from each other per color in order to enhance the luminance. However, it is difficult to entirely change the process per color to form a different optical thickness per color in a mass production process.